Preliminary evidence for upward elevational range shifts by Eastern Himalayan birds

Abstract

The ongoing climate crisis is one of the most significant threats to biodiversity globally. As the Earth warms, species have adapted by shifting their geographical ranges either polewards, or in mountainous regions, upslope towards higher elevations, presumably to continue to inhabit a suitable thermal environment. Upslope range shifts are of particular concern in tropical mountain ranges because: (a) tropical species are particularly thermally sensitive, (b) as species move upwards, they can run out of habitable space, leading to local extirpations, and (c) tropical mountains harbour a disproportionately high fraction of the planets terrestrial biodiversity - rapid upslope range shifts can therefore result in significant biodiversity losses. We used citizen science data over a 13-year period to evaluate whether 39 eastern Himalayan bird species might be shifting to higher elevations over time, by analyzing changes in the frequency of reporting of these species at birdwatching hotspots. For these species, we find evidence consistent with upslope range shifts, with species with the bulk of their elevational ranges below the hotspot elevation showing increases in their reporting frequency over time, and those with most of their elevational ranges above the hotspot elevation declining in reporting frequency. Our findings are suggestive of rapid responses to climate change by eastern Himalayan birds. We caution that eastern Himalayan bird species might be at special risk from increasing global temperatures because of their heightened thermal sensitivity coupled with particularly high rates of warming in the region. Eastern Himalayan birds are likely to require large tracts of undisturbed natural habitat across entire elevational gradients to be able to track changing temperatures by moving to higher elevations to remain resilient to climate change. SUMMARYO_LIOne of the most fundamental responses of species to changing temperatures is to change their geographic ranges, possibly to track the range of temperatures that is ideal for their survival. C_LIO_LIWith increasing climate warming, this shift could happen by moving towards the poles or in mountainous areas, towards the summit. C_LIO_LIDue to the high thermal sensitivity of tropical species and the decrease in space as species move up mountains, the extremely biodiverse bird communities of tropical mountains are particularly vulnerable. C_LIO_LIUsing citizen science data from birding hotspots along an elevational gradient in the Eastern Himalayas over a 13-year period, we measured the change in reporting frequency of 39 common bird species. C_LIO_LIChanges in reporting frequency are generally consistent with the fact that upslope shifts are taking place in the Eastern Himalayas, similar to results for birds from other tropical mountains. C_LI